1. Field of the Invention
The present invention relates to a controller for a mobile robot having a plurality of movable links extended from a base body.
2. Description of the Related Art
As a mobile robot having a plurality of movable links extended from a base body thereof, there has conventionally been known in general a humanoid robot provided with two leg links and two arm links as movable links, as described in, for example, Japanese Patent No. 5221688 (hereinafter referred to as “Patent Document 1”).
To have this type of a mobile robot perform a task at a height, it is necessary to have the mobile robot climb up and down a structure having a steep slope, such as a ladder or a stepladder (hereinafter referred to as “a steep-slope structure” in some cases).
Hence, in recent years, the research on the technology for enabling a humanoid robot to climb up and down a steep-slope structure, such as a stepladder, has been proceeding, as described in, for example, “Whole-body Climbing Motion Generation based on Body Retention Load Index and Decoupling of Physical/Geometrical Posture State Search” by Shintaro NODA, Shunnichi NOZAWA, Masaki MUROOKA, Kei OKADA, and Masayuki INABA (No. 13-2 Proceedings of the 2013 JSME Conference on Robotics and Mechatronics, Tsukuba, Japan, May 22-25, 2013/2P1-B03) (hereinafter referred to as “non-patent document 1).
To have a mobile robot, such as a humanoid robot, climb up or down a steep-slope structure, such as a ladder or a stepladder, a climbing up or down motion described below is carried out. A distal end portion of an upper movable link to be supported, which is extended from an upper portion of a base body (the distal end portion being, for example, a hand of an arm link), and a distal end portion of a lower movable link to be supported, which is extended from a lower portion of the base body (the distal end portion being, for example, a foot of a leg link), are brought into contact with the steep-slope structure thereby to support the distal end portions, and a distal end portion or portions of one or more movable links to be moved, which are different from the upper movable link to be supported and the lower movable link to be supported (e.g., one or both of other arm link and leg link), are positioned away from the steep-slope structure. In this state, the distal end portion or portions of the movable link or links are moved toward desired support position or positions and attitude or attitudes, and then the distal end portion or portions of the movable link or links to be moved are brought into contact with the steep-slope structure at the desired support position or positions and attitude or attitudes, thereby supporting the distal end portion or portions.
When the mobile robot climbs up or down the steep-slope structure, the whole center of gravity of the mobile robot normally lies at a position laterally away from the steep-slope structure. Hence, a moment (mostly a moment in the pitch direction) attributable to a gravitational force tends to act on the mobile robot.
Thus, during the execution of the climbing up or down motion, the distal end portions of the movable links supported by the steep-slope structure frequently slip. This in turn causes the actual attitude of the base body of the mobile robot to be displaced from a desired, intended attitude in many cases.
In such a case, the interference is likely to occur between a middle portion of the lower movable link to be supported, which is supported by the steep-slope structure, or a movable link to be moved (especially a movable link to be moved, which is extended from the lower portion of the base body), and the steep-slope structure. There is another possibility that the distal end portion of the movable link to be moved cannot be properly supported at the desired support position and attitude by the steep-slope structure (e.g., the distal end portion of a leg link missing a rung).